1. Field of the Invention
The present invention relates to a communication controlling process for an ATM (Asynchronous Transfer Mode) communication unit, in particular, to a path merging type communication apparatus for storing particular information contained in a pre-merged ATM cell and accomplishing a one-to-one bidirectional communication with a sender thereof in an N-to-one merging communication (where N is an integer larger than 2), a method for path marging type communication, and a storage medium storing the program which accomplishes the method.
2. Description of the Related Art
FIG. 1 shows an example of the structure of a network of an ATM switching system having a conventional ATM communication unit. FIG. 2 shows an example of the structure of the ATM communication unit. FIG. 3 shows data flows switched by the ATM switching system. The conventional ATM communication unit 8 shown in FIG. 1 is connected to other ATM communication units or ATM terminal units (or terminal units having ATM functions) (9a to 9d, 10, and 11). The conventional ATM communication unit 8 provides a one-to-one mutual communication from the unit 9d to the unit 11. In addition, the conventional ATM communication unit 8 provides an N-to-one merging communication from the units 9a, 9b, and 9c to the unit 10. In contrast, the conventional ATM communication unit 8 provides a broadcasting communication from the unit 10 to the units 9a, 9b, and 9c. The ATM communication unit 8 merges data received from the units 9a, 9b, and 9c and send the merged data to the unit 10 through one connection. The unit 10 sends the same data to the units 9a, 9b, and 9c through the ATM communication unit 8.
FIG. 2 shows the structure of the ATM communication unit 8. The ATM communication unit 8 comprises interface units (IFs) 83 and 84, a converting unit (SW) 81, and a controlling unit 82. The interface units 83 and 84 interface with each link. The converting unit 81 switches paths and channels. The controlling unit 82 controls processes for various requests (band change, line change, line expansion, and so forth) to the ATM communication unit 8. The interface units 83 and 84 comprise sending units (83s and 84s) and receiving units (83r and 83r) and can function as a leaf IF unit or a root IF unit.
The ATM system is basically a connection type data switching system. The ATM system transmits information with cells (the size of each cell is 53 bytes, fixed). At present time, each ATM communication unit connected as a network simply transmits information signals. However, in near future, services that require cooperation of each ATM communication unit will be provided. To do that, control information should be exchanged between each ATM communication unit. In each ATM communication unit, as with information signals, control signals are transmitted with cells.
A 53-byte cell is composed of a five-byte header and a 48-byte payload. The 48-byte payload stores user information. The five-byte header contains information such as a virtual path identifier (VPI), a virtual channel identifier (VCI), and a priority level. The VPI and VCI are used to identify a virtual path connection and a virtual channel connection in an ATM communication, respectively. The VPI is an identifier for identifying as a path a connection that is a part of one optical transmission link and that is statically assigned. In contrast, the VCI is an identifier for identifying as a channel a connection that is dynamically assigned in a particular VPI.
When the ATM communication unit receives a cell, it determines an input link thereof (leaf interface (IF)), an output link (root IF unit) corresponding to the header of the cell, and an output header using an internal conversion table. The ATM communication unit converts the header of the cell into the obtained header, and outputs the resultant cell to the output link. Such a switching operation is performed at very high speed by hardware or the like. To further increase the transmission speed, however, the contents of the header is limited. For example, the header does not contain the address of the terminal unit of the sender of the cell. When a cell is switched, the VPI and VCI contained in the header of the cell from the sender are substituted with a VPI and a VCI assigned to a virtual connection (VPC and VCC) between the ATM communication unit and the destination (including an intermediate ATM communication unit). Thus, in the network structure of which input data are merged by an ATM communication unit, it is impossible to determine information of input paths of pre-merged cells (the VPI and the VCI that have not been converted) and sender units of the cells from information of the merged cell.
As described above, according to the conventional method, with information of a merged cell, information of each pre-merged connection cannot be obtained. Even if a response to a particular pre-merged connection is required, a message should be sent to all connections. FIG. 3 shows an example of a data switching operation of the conventional ATM communication unit. When a controlling unit 12a of a set top box (STB) 12 connected to a terminal unit 1 that is an ATM communication unit sends an ATM cell (control cell) that contains a request (for example, a request for increasing the communication capacity of a service to a service provider 2) to an ATM communication unit 8, the ATM cell is merged with other ATM cells sent from other users. Thereafter, the merged cells reach the controlling unit 82 as denoted by an arrow A. At this point, sender information (namely, information with respect to a connection with the set top box (STB) 12 connected to the terminal unit 1) is lost. Thus, when the ATM communication unit 8 sends to the terminal unit 1 a response against the request sent from the terminal unit 1 (the response is for example permission/rejection of the request and available band), although only the terminal unit 1 requires the response, since the controlling unit 82 of the ATM communication unit 8 cannot obtain the information with respect to the connection to the STB 12, the controlling unit 82 sends the response to all the available connections.
For example, in a video conference application, while video data and audio data are being sent with a channel (VC) 1 and a channel (VC) 2, the band width of the channel (VC) 1 may be increased due to necessity of detailed video information. With a conventional ATM communication unit, a request for dynamically increasing the band of a particular channel can be issued with a control cell. As described above, however, after the control cell is merged with other cells, since the VPI and VCI for identifying the sender of the control cell and the connection with the ATM communication unit are lost, the sender of the control cell cannot be identified. Thus, information that represents the response against the request and the available band cannot be sent back to the sender. Thus, the response against the request is sent to all hardware units (all ATM communication units or terminal units with ATM functions) connected to the ATM communication unit that has sent the request as broadcasting type communication (communication flow denoted by an arrow with a dotted line shown in FIG. 1). Consequently, various problems such as the increase of loads of ATM terminal units and set top boxes, the increase of the traffic of the network, and leakage of information take place.